What is this?

Ashley • 💕 Happily married 2/23/2019 💍 Mommy to a beautiful baby girl Rileigh Grace 1/28/2020 👶🏻

Does anyone know what this white bubble thing is on my daughter's upper lip? She will be 3 weeks old tomorrow and this has been there for only maybe a week or so. Our next doctor's appointment isn't for a couple more weeks and I'm just curious as to what it is...